A number of apparatus for controllably moving a tool in order to perform a work operation are known. Examples include ink jet and thermal printers, fabric cutters, signmaking devices and plotters. Typically, such apparatus include a computer control unit for moving the too, such as a knife, pen, scribe or ink jet head, mounted on a carriage back and forth in at least one direction according to a pre-programmed set of instructions. The control unit positions the tool in the direction of movement in relation to a reference or home position, which defines the limit of movement of the tool in that direction while the apparatus is performing the work operation. Accordingly, prior to beginning the work operation, the apparatus must establish the home position to insure accurate positioning of the tool by the control unit.
In the past, a limit switch has been employed to establish the tool's home position. At the limit of the tool's movement in a respective direction, the carriage supporting the tool engages and depresses a spring loaded plunger. The plunger activates a switch which sends a signal to the computer control unit indicating that the tool has reached its limit of travel. The disadvantages associated with such an arrangement are that the spring and switch are subject to mechanical failure. Failure of the switch not only results in down time for the apparatus, but also requires the expenditure of time and expense to have the limit switch repaired.
Accordingly, it is an object of the present invention to provide an apparatus for determining the home position of a tool mounted for movement in at least one direction which does not require a limit switch for signaling that the tool has reached its limit of travel.
It is a further object of the invention to provide a method for operating such an apparatus.